Watercraft innovations in recent years have lead to the creation of a multitude of variations in hull design with consequent desire by users for variations in ramp design in their quest to protect their watercraft against potential damage when it is temporarily stored (i.e., parked) out of the water on a ramp during periods of non-use. It is gradually becoming economically impracticable for a supplier of ramps to market every conceivable variation to satisfy various customer predilections. Nevertheless, to the extent known, no one heretofore has ever figured out a way to make an economically practical watercraft ramp capable of having its hull-support assemblies essentially infinitely adjustable along the length of a channel rail, and to make the spacing of channel rails themselves also conveniently adjustable so as to permit a consumer or user to achieve essentially infinite location variations for hull-support assemblies to satisfy the user's predilection. It is to a solution of this problem that this invention is directed.